The present invention relates to a method for dissolving a powder material in a liquid and for deaerating the thus dissolved solution, or any dissolved solution, and more particularly to a method through which the powder material that tends to develop into an undissolved agglomeration is dissolved and deaerated rapidly and easily with no bubbles being developed.
The undissolved agglomerations of the powder material are suspended in the liquid with the solution surface material which is in contact with the liquid and which forms a thin gelatinous film of high density within which the powder material remains as it is. The present invention permits not only the dissolution of such agglomerations but also the aeration or defoaming of a liquid.
Conventionally various methods have been developed to dissolve the powder material that tends to agglomerate.
One of the methods is one in which the powder material is immersed for a sufficiently long time, until the material swells adequately, in a liquid of relatively low temperatures at which the agglomerations are not likely to develop, then the liquid is heated to have the powder material dissolve in the liquid. This method requires a long time for the powder material to swell in the liquid and for heating the solution to a temperature at which the powder material begins to dissolve.
Another method is one in which the powder material is added to a liquid of a relatively low temperature at which the agglomerations are not likely to develop, then the material is sufficiently dispersed in the liquid, and finally the liquid is heated for the powder material to dissolve in the liquid while being forcibly agitated.
In this method, as soon as the powder material is introduced into the liquid, the liquid is agitated so that the powder material will not produce agglomerations and is then further agitated while the temperature of the liquid is being raised to a point at which the material starts to dissolve in the liquid.
Still another method is one in which the powder material is continuously supplied into a liquid at a constant flow rate, so that the material is evenly dispersed in the liquid. The liquid is at a relatively low temperature at which the agglomerations are not likely to develop, and then the liquid is heated under forcible agitation for continuous dissolution of the powder material.
This method requires a constant flow material-feeding apparatus and a continuously dissolving apparatus. Also, the powder material tends to be deposited on the inner wall of the conduits, thus causing a resultant difficulty in operating the two apparatuses in a steady manner.
To overcome the aforementioned drawbacks, the method disclosed in commonly assigned Japanese Patent Laid-Open No. 50-97578 was proposed. This method is one in which a liquid, into which the powder material is to be dissolved, is heated to a temperature higher than that at which the powder material starts to dissolve, and then the powder material is supplied into the liquid while the tank within which the liquid is accommodated is strongly agitated at a position near the liquid surface as well as at the bottom of the liquid, thus dissolving the powder material in the liquid.
The decompression of a tank is commonly employed when deaerating a solution in the tank. That is, the pressure in the tank is reduced to allow the bubbles in the solution to rise to the surface of the solution for vanishment.
Another way of destroying the bubbles is to introduce air or an inert gas for pressurizing the solution (Japanese Patent Publication No. 63-66564).
The above-described conventional methods of dissolving the powder material suffer from the following problems:
(1) Preparing a solution of a high concentration of powder material requires a very strong agitating power which increases the potential of introducing bubbles into the solution when stirring, and, therefore, deaeration is necessitated. The deaeration methods include deaeration by elevating the bubbles to the liquid surface and deaeration by the use of ultrasound. Either of these methods requires a long preparation time of the liquid or complex process stages; and
(2) Stirring with greater power in an attempt to shorten the dissolving-time at low powder material concentrations also introduces air into the solution increasing the bubbles in the solution, thus necessitating deaeration.
Deaeration methods using only decompression of the tank suffer from the following disadvantages:
(1) The growth in volume of the bubbles in the solution due to decompression causes an increase in volume of the entire solution, thus necessitating a tank of an intolerably large size as well as placing limitations on the decompression process;
(2) Deaeration depends on the rise of the bubbles to the liquid surface; therefore, deaeration requires a long time for the bubbles to gather on the surface of the liquid so that they may be destroyed;
(3) If the viscosity of the liquid is high, the bubbles are not efficiently destroyed at the liquid surface thus causing a poor deaeration result.